The present invention relates to a rotor used in the flotation mechanism in the concentration of ores. According to the invention, upper part of the rotor chambers under the rotor cover are formed to be downward inclined from the outer edge of the chambers into the core so that they form an angle between 5 to 70 degrees with the horizontal plane. In addition the upper surface of the rotor cover can be inclined upwards raising from around the rotor shaft towards the outer edge at an angle between 5-70 degrees. With the means inside and above the rotor the slurry is directed upwards through the stator of the flotation mechanism. The developed rotor improves the suspension of coarse particles with high specific gravity within a flotation machine. The invention relates also to a method for inverting the material flow discharging from the rotor.
Flotation is essentially a three phase process involving the mixing of finely ground solids, and air to concentrate valuable minerals from gangue by floating one away from the other. Upstream to this process, water is added to the ore and fed to a comminution circuit whereby the ore is broken down and reduced in size to form a finely ground solid/liquid mixture called a slurry or pulp. The slurry is then further processed through a group or bank of flotation devices which have flotation mechanisms suitable for keeping the slurry mixture suspended while at the same time air is induced through the mechanism and dispersed evenly throughout the cell.
Suitable reagents are also added to the process that are capable of coating the surfaces of the valuable minerals to make their surfaces hydrophobic and so promote bubble/particle attachment. Once the valuable mineral particles attach to an air bubble they slowly rise to the cell surface to form a stable froth zone. This froth containing the valuable minerals is then recovered via a launder system to complete the flotation process.
For those who are experienced in the art it is generally accepted that a flotation device can be broken down into the following zones:1) a mixing zone, 2) a quiescent zone, 3) an enrichment zone and 4) a froth zone.
The mixing zone is located in the lower region of the flotation device where there is a significant zone of turbulence created by the high velocity pulp flows exiting the flotation mechanism. The quiescent zone is directly above the mixing zone and is a region where the secondary pulp (slurry) flows are of a much lower velocity and promote the upward movement of valuable mineral particles attached to air bubbles. The enrichment zone is directly under the froth zone and can extend 4 to 6 inches below the froth/pulp interface.
As the secondary pulp flows move across the cell directly underneath the enrichment zone these air bubbles together with their mineral load get the opportunity to rise up due to their inherent buoyancy and transfer into the enrichment zone before the pulp flow is redirected downwards and back into the mixing zone to repeat the cycle. Once these valuable mineral particles attached to air bubbles enter the enrichment zone the probability is high that these particles will continue to rise into the froth zone and be recovered via the launder system. However, some xe2x80x9cdropbackxe2x80x9d of valuable mineral does occur and as a consequence these particles return into the secondary flows to repeat the process if they do not collide and reattach themselves to another air bubble in the meantime.
While it is accepted that the froth zone, quiescent zone and enrichment zone are also important regions within a flotation cell it goes without saying that the mixing zone is the most important region within a flotation device for it is in this region that particle suspension and air dispersion takes place. If the flotation mechanism fails to properly disperse the air throughout the cell or if the solids suspension is inadequate then the flotation process suffers and the overall recovery of the desired minerals will be less.
A very common type of flotation mechanism consists of a rotating rotor and stator blades around the rotor. Air is fed near the rotor for example through the rotor shaft. As a result of flotation, valuable mineral particles attach to air bubbles and accumulate in a froth In the upper part of the flotation cell and is discharged through a launder of the cell. Tailings of the slurry are directed to the next separation step.
In the U.S. Pat. No. 4,078,026 there is described a rotor-stator mechanism where the rotor has both slurry and air slots separately. The main idea of the mechanism is that the rotor creates a dynamic pressure that compensates for the hydrostatic pressure developed across the height of the rotor so that the total pressure caused by the slurry to the dispersion surface is substantially equal over said surface. The main type of said mechanism is so-called OK-rotor, whose form in vertical section is downward tapered and in which vertical rotor blades are so arranged that they form separate slurry slots and air slots between the blades. Air is pumped through the hollow rotor shaft into the air slots. The rotor has a horizontal cover plate above the blades which deflects both the slurry and air flows exiting the slots in a predominantly horizontal direction. Stator vanes are predominantly vertical and help eliminate the rotational component of the flow from the rotor.
Another flotation mechanism is described in U.S. Pat. No. 4,800,017 which seems very similar to the above-mentioned system except that the function of the slots is different. The rotor body includes a horizontal top plate and a plurality of vertically oriented rotor blades which form pump chambers. Air is pumped to each chamber for aerating the pulp of the flotation cell. The stator blades are deflected outwardly from their upper part, the lower part being vertical. The discharge of the slurry flow exiting the rotor is predominantly horizontal. However, the stator incorporates a deflector vane which effectively deflects this flow downwards at approximately 15 degrees.
In the EP patent 844 911 the rotor has a horizontal barrier in the middle of the pumping chambers which again deflects both the upward and downward flows entering the rotor in a predominantly horizontal direction when discharged.
It is also know before a flotation machine which has a plurality of vertical oriented plates which form the pumping chambers. Air is pumped to each chamber via a vertical downcomer which also incorporates and supports a horizontal shroud directly above the rotor. This shroud also supports the vertical stator blades. While the slurry flow entering the rotor is initially deflected upwards as it exits the rotor pumping slots it is deflected horizontally by the overhung shroud and is pumped radially outwards through the stator blades.
In all the mechanisms described above the slurry and air flow is directed horizontally from the rotor towards the stator blades. The mechanisms are effective in the flotation of normal size particles which means that their size is less than P80=180 xcexcm (80% of the material passes a sieve of 180 xcexcm). However their performance deteriorates as the particle size and specific gravity of the mineral particles to be floated increases past this point It is also difficult to suspend particles whose specific gravity is above 3.5 t/m3. It is the object of the present invention to overcome or substantially ameliorate drawbacks of the prior art and to achieve a flotation machine whereby coarse and high specific gravity material can be effectively suspended within the mixing zone using a new style of rotor that is capable of varying the mixing flow patterns within the cell.
A new type rotor of a flotation mechanism is now developed especially for a material which is coarse and has a high specific gravity. It has been proved that a vertical section downward tapered rotor which is equipped with means to direct the slurry flow upwards instead of horizontal direction allows the rotor to vary the mixing flow patterns within the machine and without interfering with the upper enrichment and froth zones within the cell. The angle of the means with the horizontal plane is between 5 and 70 degrees, preferably between 5 and 40 degrees. It is preferable that there are also means in two levels and then it is advisable they have essentially same angle. The invention relates also to a method to incline slurry flow essentially at the same angle as that of the means itself. The essential features of the invention are apparent in the claims enclosed.
According to the invention, the flotation machine is formed of a stator having mainly vertical stator blades and a rotor which is in vertical section downward tapered and the vertical rotor blades form chambers (slots). Air is conducted to the machine through the rotor shaft and directed through the chambers into the slurry. The chambers can be common both for slurry and air or there can be separate chambers for air and slurry. The rotor blades are covered with a cover plate which reaches to the outer edge of the blades. The upper part of the chambers under the cover are now formed to be downward inclined from their outer edge into the core so that they form an angle between 5 and 70 degrees with the horizontal plane. This means that the slurry flow is inclined upwards in the chambers instead of normal horizontal direction and so the slurry flow discharging the rotor directs according to the angle of the upper part of the chamber. Secondly, it is also preferable that the rotor is equipped with means for turning the slurry flow above the rotor and then the upper surface of the rotor cover is formulated so that its outer edge is raised with proportion to the inner edge around the shaft. It is cleat that the means can be constructed so that their surface towards the slurry is either straight or curved, concave or convex.
In practice the cover of the rotor can be formed so that its outer edge reaches to the outer edge of the rotor blades but the rotor cover itself is inclined upwards. However, a conventional rotor can be modified to the rotor according to the invention simply by equipping the normal horizontal cover plate of the rotor with additional means which change the upper part of the chambers and the surface part of the rotor cover plate.
Modifying of the upper part of the chambers can take place by inserting each chamber a plate located in between the rotor blades that form the chambers. The plates are joined at their outer terminal edge to the horizontal cover plate and extend downwardly at a selected angle to their inner edge until they intersect with the vertical rotor blades in the core of each chamber. Inclining the upper part of the horizontal rotor cover can take place equipping the rotor cover with another plate situated above the rotor cover. The upper plate is directed upwards from the level of the cover plate so that around the shaft this annular outer surface plate is attached to the rotor cover plate and at its outer edge said plate is raised by a vertical plate extending up from the cover plate said plate running coaxially with that of the shaft. The outer surface plate has a sloping surface formed like a cone. For example, a conventional OK-rotor can be equipped with means or plates which limit only pumping chambers and separate air chambers reach to the horizontal cover plate.
The conventional OK-rotor does not have the upper part of the pumping chambers inclined nor does it have an inclined top surface Now the main idea of U.S. Pat. No. 4,078,026 is still in force, e.g. constant pressure prevails over the entire dispersion surface which means that the air dispersion is even along the whole height of the rotor. If the pumping or air chambers open above the horizontal plane and take the form of the outer surface plate then it means that the pressure in outer top region of the rotor is not equal with the pressure In the other dispersion surface below and as consequence air dispersion efficiency will be less since the air will exit the rotor in the region of lower pressure.